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Osteomyelitis

In osteomyelitis, there is infection of the metaphysis of long bones. The most common sites are the distal femur and proximal tibia, but any bone may be affected (Fig. 26.10). It is usually due to haematogenous spread of the pathogen, but may arise by direct spread from an infected wound. The skin is swollen directly over the affected site. Where the joint capsule is inserted distal to the epiphyseal plate, as in the hip, osteomyelitis may spread to cause septic arthritis. Most infections are caused by Staphylococcus aureus, but other pathogens include Streptococcus and Haemophilus influenzae if not immunised. In sickle cell anaemia, there is an increased risk of staphylococcal and salmonella osteomyelitis. Infection may be from tuberculosis; although rare in the UK, it needs to be considered, especially in the immunodeficient child.

Presentation

This is usually with a markedly painful, immobile limb (pseudoparesis) in a child with an acute febrile illness. Directly over the infected site there is swelling and exquisite tenderness, and it may be erythematous and warm. Moving the limb causes severe pain. There may be a sterile effusion of an adjacent joint. Presentation may be more insidious in infants, in whom swelling or reduced limb movement is the initial sign. Beyond infancy, presentation may be with back pain in a vertebral infection or with a limp or groin pain in infection of the pelvis. Occasionally, there are multiple foci (e.g. disseminated staphylococcal or H. influenzae infection).

Investigation

Blood cultures are usually positive and the white blood count and acute-phase reactants are raised. X-rays are initially normal, other than showing soft tissue swelling; it takes 7–10 days for subperiosteal new bone formation and localised bone rarefaction to become visible. Ultrasound may show periosteal elevation at presentation. MRI allows identification of infection in the bone (subperiosteal pus and purulent debris in the bone) and differentiation of bone from soft tissue infection. Radionuclide bone scan (Fig. 26.11) may be helpful if the site of infection is unclear. The X-ray changes of chronic osteomyelitis are shown in Figure 26.12.

Treatment

Prompt treatment with parenteral antibiotics is required for several weeks to prevent bone necrosis, chronic infection with a discharging sinus, limb deformity and amyloidosis. Antibiotics are given intravenously until there is clinical recovery and the acute-phase reactants have returned to normal, followed by oral therapy for several weeks. Aspiration or surgical decompression of the subperiosteal space may be performed if the presentation is atypical or in immuno-deficient children. Surgical drainage is performed if the condition does not respond rapidly to antibiotic therapy. The affected limb is initially rested in a splint and subsequently mobilised.

Summary

Presents with fever, a painful, immobile limb, swelling and extreme tenderness, especially on moving the limb